.menu {
  font-size: 14px;
  background-color: #fff;

  box-sizing: border-box;
  padding: 10px;
  width: 200px;
  height: auto;
  margin: 0;
/* use absolute positioning  */

  position: fixed;
  list-style: none;
  border-radius: 10px;
  box-shadow: 0 0 20px 0 #ccc;
  opacity: 1;
  transition: opacity 0.5s linear;
  z-index: 999;
}

.menu > li {
  cursor: pointer;
}

.menu > li:not(:last-child) {
  margin-bottom: 10px;
}